1. Field of the Invention
The present invention relates to a method for performing an etching of a stacked layer of AlCu film/TiN film with taking an oxide layer as a mask.
2. Description of Related Art
Conventionally, in order to etch a stacked layer of AlCU film/TiN film, a photo resist (PR) mask is used. At this time, a selection ratio of PR/AlCu is as small as about 1.5 to 2.
In the recent years, associated with down-sizing of wiring, a height (layer thickness) of the PR is becoming lower (thinner) in order to maintain a resolution. On the other hand, when a step is present in a device, large amount of over etching has been required in order to eliminate residual of etching due to presence of the step, facetting of the AlCu film due to etching out of the PR can be caused. Therefore, low selection ratio of PR/AlCu can be a critical factor upon etching of AlCu film toward the future. Therefore, an oxide layer mask achieving the selection ratio of PR/AlCu as high as about 5 to 10 becomes essential.
The conventional etching method of the AlCu film is illustrated in FIGS. 2(A) to 2(E). As shown in FIG. 2(A), a TiN film 2, an AlCu film 3 and a TiN film 4 are deposited on a SiO.sub.2 film 1 as an interlayer insulation layer by way of sputtering, in a sequential order, and then, an Si0.sub.2 film is deposited on the TiN film 4.
Then, as shown in FIG. 2(B), a resist film 6 is formed on the SiO.sub.2 film 5. The resist film 6 is patterned to form a mask for etching the lower SiO.sub.2 film 5.
Subsequently, as shown in FIG. 2(C), the resist film 6 is removed. Here, with taking the SiO.sub.2 film as the mask, wiring is formed.
Discussing more particularly, at first, at a first step, etching of the AlCu film 3 is performed. Here, etching is performed by using Cl.sub.2 /BCl.sub.3 /N.sub.2 /CHF.sub.3. For example, using a condition of gas flow rates of Cl.sub.2 /BCl.sub.3 /N.sub.2 /CHF.sub.3 =20 sccm/40 sccm/5 sccm/5 sccm, a pressure of 25 Pa, RF power of 650 W, etching of the AlCu film 3 is performed with forming a side wall protection film by supplying an N type deposition material to the side wall of the AlCu film 3 to form an electrode wiring 7 (FIG. 2(D)).
Next, at a second step, etching of the TiN.sub.2 film 2 is performed. At the second step, similarly to the foregoing first step, etching is performed using Cl.sub.2 /BCl.sub.3 /N.sub.2 /CHF.sub.3. For example, using a condition of gas flow rates of Cl.sub.2 /BCl.sub.3 /N.sub.2 /CHF.sub.3 =5 sccm/40 sccm/5 sccm/5 sccm, a pressure of 25 Pa, RF power of 450 W, etching and overetching of the TiN layer 2 is performed to complete the electrode wiring 7 (FIG. 2(E)).
However, the prior art illustrated in FIGS. 2(A) to 2(E) encounters a problem to cause side etching (corrosion) of the AlCu film 3 during etching of the TiN film 2 at the second step.
The reason is as follow. Namely, in case of the mask using resist film, no carbon type deposition material is supplied from the resist film. In etching of AlCu/TiN, etching is progressed with taking Cl radical as main etchant. On the other hand, in order to obtain perpendicular shape at the side wall, it is preferred to progress etching with forming a side wall protection film on the side wall of the AlCu film 3. IN case of the mask of the resist film, since the side wall protection layer can be formed on the side wall of the AlCu film 3 by supplying carbon from the resist, etching can be performed without causing corrosion of the AlCu film.
In contrast to this, in case of the oxide film mask, since the protective layer can be formed by an additive gas upon etching the AlCu film 3. However, upon etching of the TiN film 2, the effect of the additive gas becomes small to make wise wall protecting effect of the AlCu film 3 small in comparison with that in the case where the resist film is used as the mask primarily for no carbon being supplied. Therefore, reaction between the excessive Cl radical and the AlCu film is progressed to cause isotropic etching of the side wall of the AlCu film for causing corrosion.